The present invention relates to a system for producing stereographic images with a single lens. We show that this system can be extended to a microscope, to microscope ocular adapters, to a stereographic video lens, and to a stereographic adapter for any video capable device.
Optical systems such as a microscope typically produce a two-dimensional image of the subject under view. In a microscope an intermediate image is viewed through ocular eyepieces or is focused at an image plane where it may be recorded with a video camera. The usual microscope contains a single objective lens, which functions to produce a magnified image of the subject to be viewed, and either a single ocular for viewing with a single eye, dual oculars for viewing with right and left eyes, or an access hole for recording magnified images with a still or video camera. Because the image is produced with a single objective lens, the viewer has had no perception of depth.
Heretofore, proposals have been made in prior art for stereographic viewing with microscopes that use a single objective lens. All of them suffer from problems and limitations.
Carter 1988, in U.S. Pat. No. 4,761,066, proposes orthogonally opposing linear polarizing filters adjacent to the objective lens with left and right matching linear polarizing filters in the binocular oculars. This method suffers from three problems. First, the position of the orthogonally opposing linear polarizing filters are adjacent to the objective which prevents use with powers higher than 10.times.. Second, the use of linear polarizing filters in the oculars causes alignment problems when the oculars rotate as when focusing. And Third, the use of linear polarizing filters near the image plane causes distortion and visual noise from contaminants.
Greenberg 1999, in U.S. Pat. No. 5,867,312, proposes a variation on Schulman 1941, in U.S. Pat. No. 2,255,631, wherein polarized or colored light from two or more axially differentiated paths is projected either down through a single objective or up through the specimen to be viewed. The differently linearly polarized light is then viewed by the appropriate oculars thus producing a stereographic effect. This method works well at low magnifications, but produces reduced stereographic information as magnification increases. Because polarized light is transmitted through the subject, polarizing subjects can severely distort the quality or perceptibility of the perceived image. Finally note that Schulman suffers from many of the problems of dual-lens that lead to viewer discomfort.
Tandler 1998, in U.S. Pat. No. 5,835,264, utilizes an approach that parallels Greenberg 1999, wherein linearly polarized light is projected either down through a single objective or up through the specimen. This approach shares the same limitations as Greenberg 1999.
Songer 1973, in U.S. Pat. No. 3,712,199, discloses a method for producing stereoscopic motion pictures using only a single lens. That approach utilized anaglyphic filters at the aperture stop, a technique that has been demonstrated to not work well with Video. Songer 1997, in U.S. Pat. No. 5,671,007, discloses a method for producing stereoscopic video using only a single lens. That approach requires an active switching occluding device, termed a "light-valve," to be placed at the aperture stop of the lens. Use of an active element in a lens is more costly to install, more difficult to maintain, and, when it fails, significantly degrades the optical properties of the lens. The method we disclose herein places a passive system at the aperture stop of the lens. A passive system is less expensive to install, requires no maintenance, and cannot fail. Because the passive component only effects the orientation of polarization, it is essentially invisible, and thus does not change the nature of the lens unless that lens is used in conjunction with external components to create a stereographic effect. Songer also advises using an off-the-shelf light-valve, without disclosing the nature or construction of such a light valve. Such components typically use opposing polarization at the aperture stop, thus preventing them from being used to photograph the sky, water, or reflecting surfaces that effect polarization. The method we disclose herein uses a single polarizer ahead of the aperture stop, which allows those subjects to be successfully photographed.
Shipp in U.S. Pat. No. 5,471,237 discloses an active shutter mounted transversely across the optical tube. No mention is made of where in the light path such a shutter should be mounted. Like Songer above, Shipp uses an active shutter inside the lens system which produces a similar disadvantageous failure mode.
Lia in U.S. Pat. No. 5,222,477 discloses two holes on either side of a single lens. Lia confuses dual-lens with single lens technologies. His "left and right pupils" emulate the human-eye method (dual-lens) of viewing. Lia also fails to specify that the "left and right pupils" must be placed at the aperture stop or one of its conjugates.
Greening in U.S. Pat. No. 5,828,487 discloses a switching device between the lens system and the camera. Greening fails to specify that the opaque leaf must be positioned at the aperture stop or at one of the conjugates of the aperture stop. The use of a mechanical opaque shutter leads to a failure mode which causes the shutter to center and thus make the entire system unusable.
Watts in U.S. Pat. No. 5,914,810 and GB2298989 places an active "optical shutter" that "constitutes the iris" inside a lens. The active optical shutter is the same as the active light-valve above specified by Songer for motion pictures, but here used for an endoscope. This optical shutter suffers from the same drawbacks as the light-valve of Songer. The specification of the iris fails to recognize that the aperture stop or any conjugate of the aperture stop are the preferred location for the optical shutter.